EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 422/1 Article
Free access article

Issue A&A
Volume 422, Number 1, July IV 2004
Page(s) L9 - L12
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040188



A&A 422, L9-L12 (2004)
DOI: 10.1051/0004-6361:20040188

Letter

The extended star formation history of $\omega$ Centauri

M. Hilker1, A. Kayser1, T. Richtler2 and P. Willemsen1

1  Sternwarte der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
2  Universidad de Concepción, Departamento de Física, Casilla 106-C, Concepción, Chile

(Received 29 April 2004 / Accepted 28 May 2004 )

Abstract
For the first time, the abundances of a large sample of subgiant and turn-off region stars in $\omega$ Centauri have been measured, the data base being medium resolution spectroscopy from FORS2 at the VLT. Absolute iron abundances were derived for ~400 member stars from newly defined line indices with an accuracy of $\pm$0.15 dex. The abundances range between $-2.2<\rm [Fe/H]<-0.7$ dex, resembling the large metallicity spread found for red giant branch stars. The combination of the spectroscopic results with the location of the stars in the colour magnitude diagram has been used to estimate ages for the individual stars. Whereas most of the metal-poor stars are consistent with a single old stellar population, stars with abundances higher than $\rm [Fe/H]\simeq-1.3$ dex are younger. The total age spread in $\omega$ Cent is about 3 Gyr. The monotonically increasing age-metallicity relation seems to level off above $\rm [Fe/H]\simeq-1.0$ dex. Whether the star formation in $\omega$ Cen occured continuously or rather episodically has to be shown by combining more accurate abundances with highest quality photometry.


Key words: stars: abundances -- globular clusters: individual: $\omega$ Cen, M 55 -- galaxies: dwarf -- galaxies: nuclei

Offprint request: M. Hilker, mhilker@astro.uni-bonn.de

SIMBAD Objects



© ESO 2004


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.